1. Technical Field
This disclosure generally relates to computer graphics. More specifically, this disclosure relates to methods and apparatus for drawing an image with transparent regions on top of another image without using an alpha channel.
2. Related Art
Designing a circuit can be a tedious process which often requires users to spend many days editing a circuit design using a layout editor. During the design process, users routinely drag objects across the screen of the layout editor to place these objects at a precise location of the circuit design. If the user experiences a slow response from the layout editor, the user is likely to become frustrated, which can decrease productivity. Hence, it is desirable to ensure that the layout editor can move a large number of user-selected objects on the screen without any perceptible lag.
If the system supports an alpha channel for storing transparency information, the objects in the layout editor can be moved efficiently across the screen. However, many systems do not support an alpha channel, and even those that support an alpha channel often have poor performance. In such systems, some conventional techniques have an unacceptable level of lag. Other conventional techniques improve performance by only showing the outlines of the objects that are being moved, which is not ideal because users typically like to see the actual objects, and not just the outlines. Furthermore, if the number of objects that are being moved is very large, even the outline-based approach can experience an unacceptable level of lag.